1. Field of the Invention
The invention relates to a process for operating a capacitive switch, the switch having an oscillator which delivers a measurement signal, a capacitive sensor consisting of at least one sending electrode and one measurement electrode, and an evaluation circuit. In addition, the invention relates to the circuit of a capacitive switch, with an oscillator, with a gauge length and an evaluation circuit, the oscillator delivering a measurement signal and the gauge length having at least one sensor with a sending electrode and a measurement electrode.
2. Description of the Related Art
Switches, especially inductive and capacitive switches, are used in a host of very different applications in industrial engineering. They can be both switches which operate without contact, i.e. those in which the actuation object simply approaches the active surface of the switch, which are then usually called proximity switches, and also contact switches, i.e. those in which the actuation object touches the active surface of the switch. It is common to these switches that they are so-called open electronic systems, i.e. the active sensors are not entirely shielded and thus release electromagnetic radiation and signals into their vicinity and vice versa pick up electromagnetic radiation and signals from the vicinity. This circumstance can on the one hand lead to noise emissions of the switch, on the other hand to incident noise into the switch.
The aforementioned problem has been addressed in switches by on the one hand the active sensors being at least partially shielded, on the other hand by the voltage on the sensors being reduced. The two however lead automatically to a lower maximum possible object acquisition distance--generally called the operating distance--and/or to a poorer ratio of the useful signal to the noise signal.
Due to the increasing popularity of devices which emit electromagnetic radiation and signals, such as mobile telephones or remote controls, and due to increased use of switches also in the vicinity of these electromagnetic signal-emitting devices, malfunctions of switches and/or electronic devices by noise emissions and incident noise can occur to an increasing degree. One example is the use of capacitive switches in the door handles of motor vehicles, which on the one hand are disrupted by the emitted signals of a car phone and on the other hand can interfere with the car phone itself.